The present invention relates generally to medical treatments. More specifically, the present invention relates to medical fluid treatments, such as the treatment of renal failure.
Hemodialysis (“HD”) in general uses diffusion to remove waste products from a patient's blood. A diffusive gradient that occurs across the semipermeable dialyzer between the blood and an electrolyte solution called dialysate causes diffusion. Hemofiltration (“HF”) is an alternative renal replacement therapy that relies on a convective transport of toxins from the patient's blood. This therapy is accomplished by adding substitution or replacement fluid to the extracorporeal circuit during treatment (typically ten to ninety liters of such fluid). That substitution fluid and the fluid accumulated by the patient in between treatments is ultrafiltered over the course of the HF treatment, providing a convective transport mechanism that is particularly beneficial in removing middle and large molecules (in hemodialysis there is a small amount of waste removed along with the fluid gained between dialysis sessions, however, the solute drag from the removal of that ultrafiltrate is not enough to provide convective clearance).
Hemodiafiltration (“HDF”) is a treatment modality that combines convective and diffusive clearances. HDF uses dialysate to flow through a dialyzer, similar to standard hemodialysis, providing diffusive clearance. In addition, substitution solution is provided directly to the extracorporeal circuit, providing convective clearance.
Most HD (HF, HDF) treatments occur in centers. A trend towards home hemodialysis (“HHD”) exists today in part because HHD can be performed daily, which has therapeutic benefits versus in-center hemodialysis treatments, which occur typically bi- or tri-weekly. Studies have shown that a patient receiving more frequent treatments removes more toxins and waste products than a patient receiving less frequent but perhaps longer treatments. A patient receiving more frequent treatments does not experience as much of a down cycle as does an in-center patient who has built-up two or three days worth of toxins prior to a treatment. In certain areas the closest dialysis center can be many miles from the patient's home causing door-to-door treatment time to consume a large portion of the day. HHD can take place overnight or during the day while the patient relaxes, works or is otherwise productive.
Controlling the flow of dialysate to and from the dialyzer (extracorporeal circuit) is important in HD (HF, HDF). It is important to know the overall flow volume of fresh fluid pumped through the dialyzer to know how much blood clearance or potential clearance has taken place over a treatment. It is also important to know the net overall flow volume difference of dialysate removed from the dialyzer versus the volume delivered to the dialyzer to know how much excess liquid or ultrafiltrate has been removed from the patient during a treatment.
In-center machines are sterilized or cleaned chemically, which allows balance chambers or other flow control apparatus to be reused. Certain home machines have instead used a disposable pumping cassette, which is used once and discarded. The cassette operates with pump actuators to control flow. The type of volumetric control dictates the type and complexity of the disposable cassette. It is desirable to use a type of volume control that makes the disposable cassette as simple and cost effective as possible.